Curl corrector apparatus for operating on a continuous web

ABSTRACT

A curl corrector apparatus has corrector rods around which a continuous web is trained, as it is being unwound, to remove residual curl. These rods are adjustable and are moved to the most effective correcting position in response to signals derived from the web downstream of the corrector rods. When the web is subsequently cut into sheets, any curl in these sheets can be detected, preferably optically or sonically, and corrective signals obtained. When the web is continuous, mechanical sensing means can detect the direction in which the web tends to bow and hence provide a corrective signal.

United States Patent Bossons et al.

[ Mar. 26, 1974 CURL CORRECTOR APPARATUS FOR OPERATING ON A CONTINUOUS WEB [75] Inventors: Walter Howard Bossons; Horst Karl Lindstaedt; Graham Robin Scott Jones, all of Bristol, England [73] Assignee: Masson Scott Thrissell Engineering Limited, Bristol, England [22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,226

[30] Foreign Application Priority Data Mar. 27, 1971 Great Britain 8197/71 [52] US. Cl. 93/1 R, 162/197 [51] Int. Cl. 831d [58] Field of Search 93/1 R; 162/252, 197, 270, 162/271 [56] References Cited UNITED STATES PATENTS Gurley et al. 4. 112/252 5/1972 Shelor 162/271 8/1960 Carry 83/102 X 5 7 ABSTRACT A curl corrector apparatus has corrector rods around which a continuous web is trained, as it is being unwound, to remove residual curl. These rods are adjustable and are moved to the most effective correcting position in response to signals derived from the web downstream of the corrector rods. When the web is subsequently cut into sheets, any curl in these sheets can be detected, preferably optically or sonically, and corrective signals obtained. When the web is continuous, mechanical sensing means can detect the direction in which the web tends to bow and hence provide a corrective signal.

PATENTED M826 I974 SHEET 1 [IF 5 PATENTED R26 I974 SHEET 2 BF 5 I PATENTEDHARZB I974 SHEET 3 [1 5 8m Em C. 1 5 w CURL CORRECTOR APPARATUS FOR OPERATING ON A CONTINUOUS WEB This invention relates to curl corrector apparatus for operating on continuous running webs of paper, cardboard or like material. Such materials generally tend to curl as a result of having been previously stored in reel form. Curl corrector apparatus is known in which a curl corrector rod is arranged to bear on the running web so as to deflect it in the direction opposite to that in which the web tends to curl. The curl corrector rod is usually displaceable transversely to the path of the web to vary the curl correcting effect of the rod. The correct adjustment of the rod to eliminate residual curling effect in the material requires skilled and careful attention on the part of the operator. The curl correcting apparatus is principally used in conjunction with a cutting apparatus which cuts the web into individual sheets, in which case the residual curling effect may not be visible until the material has been cut. By the time the operator has noticed a residual curling effect in the cut sheets and re-adjusted the curl corrector apparatus, a large number of sheets may have been produced with an unacceptable amount of curl in them. Furthermore, the operator s corrective adjustment may not have the desired effect first time.

It is an object of the present invention to provide an automatic curl corrector apparatus which will reduce the need for skilled attention and which may react faster than a manual system to correct a residual curling effect.

According to the present invention, a curl corrector apparatus for operating on a continuous running web of paper, cardboard or like material comprises a curl corrector rod arranged to bear on the running web, means for displacing the rod transversely to the path of the web to vary the curl correcting effect of the rod, means for sensing residual curling effect in the material after it has passed the curl corrector rod and for producing a signal related to the curling effect sensed, and means for feeding back the signal to provide a closedloop control of the rod displacing means. The sensing means may be electronic, optical, sonic, mechanical or any combination of these, and be arranged to detect the presence of curling effect, its magnitude and direction. It may be arranged to sense the curling effect in the continuous web or in individual sheets after the web has been cut.

A device which senses residual curl in a continuous web may consist of follower rolls on pivoted arms which are sensitive to the tendency of the web to adopt its natural curl.

A device which senses residual curl after the web is cut may be sensitive to the edge profile of a sheet either as it passes through draw rolls after being cut or as it is supported on a conveyor prior to being stacked. Such a device may operate on photoelectric or sonic principles, the sensing means in either case being sensitive to its separation from the area on the sheet at which it is directed. This separation will vary with time in a manner depending on the degree of curl present in the sheets and also on the direction of the curl. In the case of a photoelectric device the intensity of light reflected by the surface of the sheets and received by a photosensitive device will vary with time in a manner related to the residual curl present in the sheets. In the case of a sonic device the transit time of a transmitted sonic pulse reflected from a small area on the surface of the sheet and received by a suitable sonic receiver will also be a measure of the separation between the sensing device and the area on the sheet at which the sonic pulse is directed. Alternatively a Doppler radar principle may be used to monitor the rate of change of said separation, and therefore edge profile, with time.

Preferably two curl corrector rods are provided, disposed on opposite sides of the continuous web and both connected to the rod displacing means, so as to be capable of correcting curl in either direction, e.g., as described in our co-pending British application No: 6522/71.

The invention may be performed in various ways and some specific embodiments will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic elevation of an installation for correcting the curl in a continuous running web and for cutting the web into individual sheets which are subsequently overlapped preparatory to being stacked, the curl sensing means being shown to a larger scale at A and B,

FIG. 2 is a graphical representation of the signals produced by the curl sensing means corresponding to the conditions of the sheets shown at A and B in FIG. 1,

FIG. 3 is a diagrammatic sectional view of a similar installation in which the curl sensing means is located immediately after the cutting means, this Figure also including representation of signals corresponding to various sheet conditions,

FIG. 4 is a diagrammatic elevation similar to FIG. 1 of a third installation, also including enlarged views of the curl sensing means at A and B and representations of the signals produced, and

FIG. 5 shows block circuit diagrams of optical control circuits FIG. 5a being a circuit associated with curl detection from one side of the sheets and FIG. 5b a corresponding circuit for detection from both sides,

FIG. 6 shows block circuit diagrams of sonic control circuits FIG. 6a being a circuit associated with curl detection from one side of the sheets, FIG. 6b a corresponding circuit for detection from both sides, and FIG. 6c a circuit using the Doppler effect rather than transit time, and

FIG. 7 is a diagram of a mechanical curl sensing device.

As shown in FIG. 1, a web W passes through a curl corrector apparatus 10, adjusted by a motor 11, to a cutting apparatus 12. The corrector apparatus 10 is described in more detail with reference to FIG. 3 below, and is preferably of the kind even more fully described in our co-pending British application No: 6522/71. The cutting apparatus 12 may be of any known type. The cut sheets (not shown) are transported to a slow conveyor 13 on which they are overlapped. Conveyor 13 comprises a series of laterally spaced bands and has upper and lower runs 131 and 132 between which the sheets 8 are trapped and carried along.

A photo-electric sensing device generally indicated at 14 and comprising a light source 15 and a photosensitive device 16 (see the detail views at A and B) is disposed above the conveyor 13 on which the sheets are overlapped. The upper run 131 of the conveyor is raised by being trained round guide rollers 133 at this point to allow the sheets S to curl if there is any residual curling effect in them. The photo-sensitive device 16 receives reflected light from the sheets S illuminated by the light source 15.

It can be seen from FIG. 2 how the intensity of the reflected light received by the device 16 varies with time according to the residual curling effect in the sheets S. Where the leading edges of the sheets tend to curl upwards as shown at A, the signal produced is typically of reversed saw-tooth form as shown in the upper one of the three representations in FIG. 2. When the sheets lie flat, the signal is of a much flattened reversed saw-tooth form within a narrow tolerance zone as shown in the middle one of the three representations. When the edges of the sheets tend to curl downwards, as shown at B, the signal consists of a series of humps, as shown in the lower representation.

The signal from the photo-electric device 16 is fed to an electronic processing device indicated at 17 which can distinguish between the three typical signals shown in FIG. 2 and which produces an output signal varying in accordance with the magnitude and direction of the residual curl in the sheets S. The output from the processing device 17 is fed back to the motor 11 so as to adjust the curl corrector apparatus in the correct sense, by the required amount and at the required rate to minimize the residual curling effect and thereby to reduce the signal from the sensing device 14 to within the permitted limits represented by the tolerance zone.

The output from the sensing device 14 may also be employed to operate a diverter 18 which rejects excessively curled sheets down a diverter chute 19 to a reject stack.

The installation illustrated in FIG. 3 differs from that of FIGS. 1 and 2 in that the photo-electric sensing device 14 is disposed immediately after the cutting means 12, so as to sense the curl in the sheets S before they have been overlapped. In other respects the installation is similar to that of FIGS. 1 and 2. FIG. 3 shows how the web W, having been drawn from a reel (not shown) is passed between guide rollers 20, 21 at the entry to the curl corrector apparatus generally indicated at 10. This incorporates a pair of curl corrector rods 22, 23 disposed on opposite sides of the web W and carried by mounting elements 24 on pivotal arms 25, 26. These arms are capable of moving the corrector rods to either side of the straight line path of the web W between the guide rollers 20, 21 and a further pair of guide rollers 27, 28 towards the delivery end of the apparatus 10 for correcting curl in either direction. Means such as the lead screw indicated at 29 driven by the motor 11 are provided for moving the mounting elements 24 transversely to the path of the web to vary the curl correcting effect exerted by the rod 22 or 23 in use.

From the curl correcting apparatus 10, the web W passes through the cutting apparatus generally indicated at 12 and comprising draw rolls 30 and cutter drums 31 which are of known type, which cut the web into individualsheets S which are subsequently overlapped and formed into a stack. Although FIG. 3 shows a double rotary type of cutter, a single rotary cutter with only one cutter drum could equally well be used.

The installation of FIG. 4 differs from that of FIGS. 1 and 2 only in that two photo-electric sensing devices 141 and 142 are used, one above and one below the conveyor 13 and spaced apart along its length. The upper run 131 is raised by guide rollers 133 adjacent the upper sensing device 141 and the lower run 132 is lowered by guide rollers 134 adjacent the lower sensing device 142. The signals received by the processing device 17 are then always of saw-tooth form, reversed for opposite directions of curl, which makes it easier to arrange for control of the motor 11 in opposite directions.

The general arrangement with sonic detecting devices is similar, and in the drawings the only change would be a sound transmitter substituted for the light source and a receiver for the photo-sensitive device. Separate general illustrations of these are not therefore provided.

Electronic processing devices for the optical and sonic systems outlined above are shown in block diagram form in FIGS. 5 and 6 respectively.

FIG. 5(a) shows the circuit for a single photocell on one side of the sheets only (FIGS. 1 and 2). The output from the photocell 16 is applied to a differentiator 51 and to an amplifier and threshbold detector unit 52. The outputs of these govern a polarity switch 53 whose two outputs, indicated as positive and negative, cause the rod adjusting motor to rotate in one or the other direction. If a saw-tooth wave form appears the differentiated signal in pulse form alters the polarity switch from one state to the other and if the signal passed by the unit 53 is beyond the threshbold, there is an output signal from the switch 53. If the humped signal is present, there is a lack of pulses from the differentiator which causes the polarity switch to revert to said one state. An output is again delivered if the amplitude is above the threshbold. A similar arrangement will work for FIG. 3 where pulses are obtainable from upward curling sheets but not from downwardly curling ones.

FIG. 5(b) shows a circuit for photocells on both sides of the sheets, as in FIG. 4. Here, the two photocells 16 feed inputs of a polarity sensor 54 and of a polarity switch 55. The latter has an output to an amplifier 56 with a deadband. The sensor 54 can discriminate between the positive or negative going vertical or sloping edges of the saw-tooth wave forms and its output triggers the polarity switch accordingly to pass the appropriate signal. If this is outside the deadband of the amplifier 56, a corrective signal is applied to the motor 1 1.

FIG. 6(a) shows a circuit for a sonic system with a transmitter and receiver on one side only. An ultrasonic oscillator 61 feeds a transmitter 62, whose reflected signals from the sheets are picked up by a receiver 63. The output of oscillator and receiver are applied to a phase comparator 64 which thus provides a signal indicative of the sonic path length at any instant. This signal is fed to a differentiator 65 and an amplifier and threshbold detector.66 which together govern a polarity switch 67 in the same manner as the circuit 51, 52 and 53 of FIG. 5(a).

FIG. 6(b) shows a circuit for a sonic system with a transmitter 62' and receiver 63' on both sides, the transmitters being governed by a common oscillator 61 Each receiver has an associated phase comparator 64' so that there are two outputs available for application to a polarity sensor 68 and a polarity switch 69 in a circuit similar to that of FIG. 5(b).

FIG. 6(a) shows a sonic system using the Doppler effect. An oscillator 81 governs a transmitter 82 whose reflected signals are picked up by a receiver 83 and applied, to one input of a beat frequency oscillator 84 whose other input is from the oscillator 81. This beat frequency is fed to a frequency-to-voltage converter 85 whose output represents the rate at which the web is moving towards or away from the receiver. In order to determine the correct sense the phase of the basic oscillator signal and the beat frequency are compared in a comparator 86 which actuates a polarity switch 87 to direct the output of converter 85 into the correct channel for correcting action. An amplifier 88 with a deadband passes the signal, if of sufficient amplitude, to the motor.

Instead of sensing the curl in the sheets S, a mechanical sensing device may be arranged to sense the curling effect in the continuous web after it has passed from the curl corrector rod and through a pair of draw rolls. Such a mechanical sensing device is shown diagrammatically in FIG. 7(a). It is considered that this will be more readily applicable to stiff webs such as cardboard rather than paper.

The web W is directed in a normally straight line path between two pairs of guide rolls 71 and 72. At a substantially central point along this run they are lightly nipped between two web follower or sensing rolls 73, 74 mounted between ends of links 75, 76 pivoted to a fixed structure at their other ends. Springs 77 acting between the links 75 and 76 at each side of the web produce the light nipping force, and this roll-link-spring assembly is of as low inertia as practicable. Means such as a coil 78 are provided with an armature 79 which is connected to the links 76 are provided to oscillate the rolls vertically, transverse to the plane of the web. An alternating current source 80 is connected to the coil 78 to produce this movement.

This arrangement can be used in two different modes to sense the curl. In each case, the web will be more resistant to movement in one direction than another due to the tendency of the web to bow according to the residual curl. In one mode a uniform alternating current is applied, but the result of the different resistances will be that the follower rolls 73, 74 will move asymmetrically with respect to the straight line path, having a greater excursion on that side to which the web tends to bow. Means such as optical sensing devices 91 can detect when this excursion exceeds a given tolerance and a resulting signal from one or other of those devices can be used to adjust the curl corrector rods.

In the other mode the rolls 73, 74 are made to oscillate symmetrically to opposite sides of the straight line path and the voltage necessary to achieve this is monitored and its asymmetry due to the existence of residual curl can provide a correcting signal.

We claim:

1. Apparatus for processing sheet material comprising a curl corrector device for operating on a continuous running web of paper, cardboard or like material and including an elongated member over which the web runs and means for displacing said member transversely to the path of the web to vary the curl correcting effect of said member, cutting means downstream of the curl corrector device for cutting the web into individual sheets, means for conveying the sheets away from the cutting means in a generally horizontal path, substantially continuous beam transmitting and receiving means focused on the conveying means, and means for feeding back the received beam signal, which varies as the curl of the sheets on the conveying means, to the curl corrector displacing means, the feedback means including means for discriminating between different signal waveforms characteristic of different directions of curl and means for applying to the displacing means a signal whose effect will be to move said member in the direction required to reduce the curl.

2. Apparatus according to claim 1, in which the beam transmitting means produces a light beam and the receiving means is photo-sensitive.

3. Apparatus according to claim 1, in which the beam transmitting means produces a sonic, pulsed beam and the receiving means is acoustically sensitive.

4. Apparatus according to claim 3, in which the discriminating means are adapted to sense the transit time of the sonic pulses to and from sheets on the conveying means and to produce signals indicative of the separation of the transmitting and receiving means from the sheets.

5. Apparatus according to claim 3, in which the discriminating means are adapted to sense the transit time of the sonic pulses to and from sheets on the conveying means and to produce signals indicative of the rate of change of separation of the transmitting and receiving means from the sheets.

6. Apparatus according to claim 1, and further comprising a diverter responsive to said discriminating means for diverting excessively curled sheets to a disposal region.

7. Apparatus according to claim 1, including means for driving the conveying means at a speed such that sheets delivered from the cutting means overlap on the conveying means. 

1. Apparatus for processing sheet material comprising a curl corrector device for operating on a continuous running web of paper, cardboard or like material and including an elongated member over which the web runs and means for displacing said member transversely to the path of the web to vary the curl correcting effect of said member, cutting means downstream of the curl corrector device for cutting the web into individual sheets, means for conveying the sheets away from the cutting means in a generally horizontal path, substantially continuous beam transmitting and receiving means focused on the conveying means, and means for feeding back the received beam signal, which varies as the curl of the sheets on the conveying means, to the curl corrector displacing means, the feedback means including means for discriminating between different signal waveforms characteristic of different directions of curl and means for applying to the displacing means a signal whose effect will be to move said member in the direction required to reduce the curl.
 2. Apparatus according to claim 1, in which the beam transmitting means produces a light beam and the receiving means is photo-sensitive.
 3. Apparatus according to claim 1, in which the beam transmitting means produces a sonic, pulsed beam and the receiving means is acoustically sensitive.
 4. Apparatus according to claim 3, in which the discriminating means are adapted to sense the transit time of the sonic pulses to and from sheets on the conveying means and to produce signals indicative of the separation of the transmitting and receiving means from the sheets.
 5. Apparatus according to claim 3, in which the discriminating means are adapted to sense the transit time of the sonic pulses to and from sheets on the conveying means and to produce signals indicative of the rate of change of separation of the transmitting and receiving means from the sheets.
 6. Apparatus according to claim 1, and further comprising a diverter responsive to said discriminating means for diverting excessively curled sheets to a disposal region.
 7. Apparatus according to claim 1, including means for driving the conveying means at a speed such thAt sheets delivered from the cutting means overlap on the conveying means. 